Investigations in our laboratoy deal with problems of mammalian developmental genetics; they are focussed on the genetic control of differentiation and the correlation of morphogenetic and functional aspects of development. These studies rely heavily on the choice of model systems suitable for experimental analysis. Mutations in the mouse with effects on embryonic development and differentiation have for many years served this purpose. The following topics are included in our proposal: 1. Genetic control of cellular interactions in mammalian differentiation. 2. Genetic control of differentiation of specific cell types. 3. Genetic control and correlation of biochemical differentiation and ultrastructural morphogenesis im mammals. In the pursuit of these problems, standard methods of chemistry, experimental embryology, histology, histochemistry, biochemistry an electronmicroscopy will be used.